1. Field of Endeavor
The present invention relates to microfluidic devices and more particularly to microfluidic devices for generating and trapping monodisperse microdroplets in a microfluidic channel.
2. State of Technology
Microfluidic devices are poised to revolutionize environmental chemical, biological, medical, and pharmaceutical detectors and diagnostics. “Microfluidic devices” loosely describes the new generation of instruments that mix, react, count, fractionate, detect, and characterize complex gaseous or liquid-solvated samples in a micro-optical-electro-mechanical system (MOEMS) circuit manufactured through standard semiconductor lithography techniques. These techniques allow mass production at low cost as compared to previous benchtop hardware. The applications for MOEMS devices are numerous, and as diverse as they are complex.
As sample volumes decrease, reagent costs plummet, reactions proceed faster and more efficiently, and device customization is more easily realized. By reducing the reaction volume, detection of target molecules occurs faster through improved sensor signal to noise ratio over large, cumbersome systems. However, current MOEMS fluidic systems may only be scratching the surface of their true performance limits as new techniques allow for repeatable generation and manipulation of nano-scale and pico-scale microfluidic reactors, loosely termed “microdroplets.” Some popular monodisperse (same size) microdroplet generating techniques include flow focusing and the T-junction, both of which employ the water-in-oil emulsion method for generating discrete aqueous chemical and/or biological reactors, at volumes previously unheard of. For example, droplets tens of microns in diameter contain a volume in the tens of picoliters. These tiny volumes, when properly controlled, enable revolutionary science, such as: single cell isolation and analysis, single molecule detection, nucleic acid amplification from single genome copies, in-vitro protein translation, microdroplet protein crystallization, and other novel techniques. The ability to generate monodisperse droplets has been crucial for optical calibration and droplet manipulation since a polydisperse distribution of droplets changes the optical interrogation performance, as well as altering the chemical kinetics of reactions within the droplets due to differing analyte quantities.
To date, the limitation of monodisperse microdroplet generation has been that it is a steady-state phenomenon, generating typically hundreds to thousands of microdroplets per second. This causes a problem when the stream of droplets needs to be slowed down or stopped for subsequent on-chip manipulation, energy deposition, chemical reaction, or optical interrogation and analysis. Prior art has been limited to employing droplets only in analyses that can happen at very short timescales, which excludes many interesting problems that would benefit from the perfect isolation the spherical aqueous microreactors can provide.